CN109070451B

CN109070451B - Temperature control before melting

Info

Publication number: CN109070451B
Application number: CN201680085116.7A
Authority: CN
Inventors: X·维拉约拉萨纳; A·M·德彭纳; S·佩加拉多阿兰门迪亚; D·兰米瑞兹姆拉; L·加西亚
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2016-05-12
Filing date: 2016-05-12
Publication date: 2020-12-15
Anticipated expiration: 2036-05-12
Also published as: US10632672B2; KR102129723B1; EP3426465A1; CN109070451A; EP3426465B1; JP6643503B2; US20190143586A1; JP2019513596A; WO2017194122A1; KR20180126057A; BR112018072109A2

Abstract

In an example, a method includes: measuring a temperature of a molten region and a temperature of a non-molten region of the first layer of build material; determining a pre-heat setting for a subsequent layer of build material in response to the measured temperature of the non-molten region of the first layer; determining printing instructions for applying a printing agent to a subsequent layer of build material, wherein, in response to the measured temperature of the melted region of the first layer, the application of printing agent specified by the printing instructions for the subsequent layer causes the temperature of the preheated build material to be a preheat temperature prior to melting; forming the subsequent layer of build material; preheating the subsequent layer of build material according to the preheating setting; and selectively applying the printing agent to the subsequent layer based on the printing instructions.

Description

Temperature control before melting

Background

Additive manufacturing techniques can generate three-dimensional objects on a layer-by-layer basis by solidifying build material. In an example of such a technique, the build material is supplied in a layer-by-layer manner, and the solidification method may include heating the layer of build material to cause melting in selected regions. In other techniques, other curing methods such as chemical curing methods or adhesive materials may be used.

Drawings

Non-limiting examples will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a flow diagram of an example method of determining printing instructions for applying a printing agent;

FIGS. 2a to 2d are schematic diagrams of exemplary thermal/print maps;

fig. 3 is a simplified schematic diagram of an example additive manufacturing apparatus; and

FIG. 4 is a simplified schematic diagram of an example processor associated with a machine-readable medium.

Detailed Description

Additive manufacturing techniques may generate three-dimensional objects by solidifying build material. In some examples, the build material may be a powdered particulate material, which may be, for example, a plastic, ceramic, or metal powder. The properties of the generated object may depend on the type of build material and the type of curing mechanism used. The build material may be deposited, for example, on a build platform and processed, for example, layer by layer within a fabrication chamber.

In some examples, selective curing is achieved by directional application of energy, for example using a laser or electron beam that causes curing of the build material upon application of directional energy. In other examples, at least one printing agent may be selectively applied to the build material. For example, coalescing agent (hereinafter "fusing agent") may be selectively distributed onto portions of a layer of build material in a pattern derived from data representing a slice of the three-dimensional object to be generated (which may be generated, for example, from structural design data). The coalescing agent may have a composition such that when energy (e.g., heat) is applied to the layers, the build material coalesces (melts) and solidifies according to the pattern to form a slice of the three-dimensional object. In other examples, coalescing may be achieved in some other manner.

In addition to the fusing agent, in some examples, the printing agent may also include a coalescence modifier agent (hereinafter referred to as "refiner") that serves to reduce or amplify the fusing action. For example, the refiner may reflect incident energy to prevent melting of the build material. The refiner may be used to control the surface finish of the object. In some examples, the fusing agent and/or the refining agent may be referred to herein as an agent and/or a printing agent.

As described above, the additive manufacturing system may generate the object based on the structural design data. This may involve the designer generating a three-dimensional model of the object to be generated, for example using a computer-aided design (CAD) application. The model may define a solid portion of the object. To generate a three-dimensional object from a model using an additive manufacturing system, model data may be processed to generate parallel-planar slices of the model. Each slice may define a portion of a respective layer of build material to be solidified or caused to coalesce by the additive manufacturing system.

Fig. 1 is an example of a method, which may be a method of additive manufacturing, the method comprising: in block 102, the temperature of the molten region and the temperature of the non-molten region of the first layer of build material are measured. A first layer of build material may be provided on the build platform, directly or overlaid on at least one previously formed layer (and in some examples, the previously formed layer may have been treated by applying at least one printing agent and irradiated with energy from an energy source such as a heat lamp).

In some examples, a plurality of temperatures on a surface of a first layer of build material can be measured to form a temperature profile. For example, the first layer of build material can be considered a plurality of pixels, and each of the plurality of pixels can be associated with a temperature measurement. In one example, the pixels are approximately 1-2cm in length, which divides a build platform of approximately 30cm by 30cm into a matrix of approximately 32 by 32 pixels, although larger or smaller pixels may be formed. In some examples, the temperature of the first layer may be measured after the processing of the first layer. The temperature may be measured by using any type of temperature sensor. In some examples, the temperature may be measured by using a thermal imaging camera or an Infrared (IR) camera. The locations of the melted and non-melted regions may be determined, for example, based on object model data or identified from measured temperatures.

Block 104 includes: a preheating setting for the subsequent layer of build material is determined in response to the measured temperature of the non-melted region of the first layer. The preheat setting determined in block 104 may be modified from the preheat setting applied to the first layer in response to the measured temperature of the non-melted regions of the first layer. The build material may be preheated using an array of preheat lamps provided on the build platform. The preheat setting specifies a preheat temperature for the build material. The pre-heat temperature is set to be lower than the melting temperature of the build material so that the build material does not melt. However, by preheating the build material, the additional energy required to raise the temperature of the build material from the preheating temperature to the melting temperature in order to melt the build material is reduced. The array of preheat lamps may be operated in unison such that they each output the same power in order to ensure that the build material within the layer is at a uniform temperature. The power output by the preheat lamp may be controlled by using Pulse Width Modulation (PWM) that is set to provide a desired level of preheat. Thus, the preheat setting may be a duty cycle of the preheat lamp. Thus, in some examples, predicting a layer of build material may include temporarily applying energy to such layer with at least one energy source as described herein. In some examples, the preheat setting may be used to adjust the power of the preheat lamp by changing the PWM duty cycle, thereby increasing or decreasing the temperature of the build material. For example, if the measured temperature of the non-melted regions of the first layer is higher than the expected temperature, the duty cycle may be reduced in order to lower the temperature of the non-melted regions. This avoids the non-melting region from being unintentionally melted when the output of the preheating lamp does not coincide with the desired output. Conversely, if the measured temperature of the non-melted regions of the first layer is lower than the expected temperature, the duty cycle may be increased in order to increase the temperature of the non-melted regions. This therefore minimizes the energy required to cause melting of the build material in subsequent layers. The difference in the measured temperature of the non-melted region from the expected temperature may be due to changes that occur during the time it takes to print the object. For example, the ambient temperature may change or the output of the preheat lamps may change as they age. The preheat lamp may be controlled based on a comparison of the measured temperature with a preset temperature and by using a suitable control method such as proportional-integral-derivative (PID) control, machine learning algorithms, proportional control, and the like. The temperature of the non-melting region may be measured at multiple locations and the operation of each preheat lamp may be adjusted to account for variations in the power output of the lamp.

Block 106 includes: print instructions for applying a printing agent to a subsequent layer of build material are determined. The printing instructions may be derived from object model data representing the object to be generated. Such object model data may, for example, comprise a computer-aided design (CAD) model, and/or may, for example, be a Stereolithography (STL) data file, and may, for example, specify material distribution (e.g., identify solid portions) in a "slice" of the object. In response to the measured temperature of the melted region of the first layer, the application of the printing agent specified by the printing instructions for the subsequent layer causes the temperature of the preheated build material to be a predetermined temperature prior to melting. In some examples, applying the printing agent to the build material may cause the build material to temporarily cool below the preheat temperature through convective heat transfer with the printing agent. If the printing agent is sufficiently applied prior to the melting stage, the build material may be returned to the pre-heat temperature. However, if the printing agent is applied immediately before melting, the temperature may not have sufficient time to return to the preheat temperature. It is to be understood that the energy required to achieve melting depends on the temperature of the build material. Thus, the cooling effect of the printing agent may be utilized in order to provide a local change in temperature prior to melting. For example, the order in which the printing agent is applied to the layers may be configured to provide a predetermined temperature profile on the surface of a subsequent layer prior to melting. This may be used to offset the change in the temperature profile measured for the first layer in block 102. For example, if the preheat lamp array produces a portion of the build material that is hotter than expected (possibly due to anomalous lamps), then that portion may overheat during melting. This problem can be counteracted by: the temperature of the build material on the part is reduced by applying the printing agent at a suitable time prior to melting in order to achieve the desired level of cooling. For example, the printing agent may be applied to the portion at the end of the application process such that it does not have sufficient time to recover. Alternatively, where the printing agent application process is sufficiently fast, it may be necessary to apply the printing agent to the portion at the beginning of the application process in order to allow sufficient time for heat loss to occur.

Block 108 includes: a subsequent layer of build material is formed. Subsequent layers of build material are laid on the previously formed first layer.

The block 110 includes: the subsequent layers of build material are preheated according to the preheating settings determined in block 104.

The frame 112 includes: the printing agent is selectively applied to subsequent layers based on the print instructions determined in block 106.

After the printing agent has been applied to the subsequent layer, energy may then be applied to the preheated build material, for example, by using an energy source, to raise the temperature of the build material above the melting temperature over a portion of the layer to form a melted region and a non-melted region. This may include, for example: applying heat to the layer of build material, such as by using heat lamps; or irradiating the layer with light, microwave energy, or the like. As will be appreciated, the molten region formed by this operation may be referred to as a "part region," where the part region of each layer may correspond to a cross-section of the three-dimensional object to be formed.

In some examples, a subsequent layer of build material may be formed, for example, to cover the agent treated and at least partially melted first layer, and the temperature of the subsequent layer may be measured, for example, prior to applying any printing agent thereto.

The application of the printing agent can also be controlled so as to vary the amount of printing agent applied to the surface of the layer so as to vary the cooling effect of the printing agent. This can be achieved by combining different reagents in different ratios.

In some examples, the measured temperature is compared to a modeled expected temperature. This may include, for example: comparing the measured temperature profile (i.e., the heat map) of the region or layer to the modeled temperature profile; or compare its spatially aligned pixels. In other examples, determining the temperature condition may include: the temperature at each of the at least one location or region on the layer is compared to a threshold temperature.

In some examples, there may be an initial set of printing instructions associated with the layers of the object to be generated, the specified amount and/or placement of printing agent for each layer. The printing instructions may be derived by using a thermal model of the object generation process. In practice, even if a thermal model is considered, the thermal behavior of the layer of build material in object generation may deviate from the model, for example due to variations in the thermal properties of the build material and/or printing agent used (e.g., the build material may be recycled and its thermal properties may change over its lifetime), environmental conditions (including ambient temperature and humidity), incomplete models, and so forth. Thus, the initial set of printing instructions may cause defects in the printed object, for example undesirable physical properties such as brittleness, loss of strength, loss of dimensional accuracy and/or increased roughness, or changes in the appearance of the object due to overheating/exposure to heat during formation of the object. Thus, the predetermined printing instructions for applying the printing agent to the subsequent layer may be modified based on the measured temperature for the first layer, as described above.

In some examples, subsequent layers may be considered the first layer in fig. 1 after melting, and the method may be performed with respect to each or at least some of the layers formed in additive manufacturing.

Fig. 2a shows an example of temperature measurement on the surface of a layer of building material as a "heat map" 200 a. Such a map may represent a plurality of imaging pixels, each imaging pixel being associated with a temperature measurement. In fig. 2a, higher temperatures are indicated as darker areas and lower temperatures are indicated as lighter areas.

Figure 2a shows a thermal map 200a of a layer of build material that has been treated with a fusing agent and heated with a heating lamp. For the purposes of this example, the object formed in this layer includes a rounded rectangular cross-section 202. As shown by the darker areas, the layer of build material is hotter on the rectangular portion 204. It is expected that the post-melt temperature of the layer will be uniform over the rectangle and the hotter portion 204 may be off the expected temperature. The hotter portion 204 may be the result of some anomaly, such as a pre-heat lamp, a difference in energy source or build material, or any other reason. The temperature of the surrounding non-melted build material is lower than the temperature of the melted region. It should be noted that in practice there may be more temperature variations, which are not shown in the drawings to avoid overcomplicating the drawings.

Figure 2b shows a printed graph depicting the application of a fusing agent to a subsequent layer of build material formed on top of the first layer shown in figure 2 a. In this figure, the darker areas represent higher concentrations of the melting agent, but are applied at lower volumes per pixel/voxel; and lighter areas indicate lower concentrations of the melting agent, but at higher volumes per pixel/voxel. As shown, the melt agent is applied in a lower concentration, but in a larger volume, on the hotter portion 204 shown in FIG. 2 a. The increased volume of the fusing agent increases the amount of heat dissipated from the preheated build material and the underlying molten layer. Thus, the cooling effect of the applied molten agent is configured to be greater on the hotter portion 204 than on the rest of the object. Thus, the application of the fusing agent is configured to counteract local changes in temperature. Although the volume of the melting agent varies over the surface of the layer, the variation in concentration ensures that the effect of the melting agent is consistent during subsequent melting of the layer. The melting agent may also be diluted by applying a refining agent to the same region. The addition of the refiner does not affect the absorption of energy during melting, but the additional volume of refiner enhances the cooling effect of the printing agent. Thus, the concentration of the melting agent can be adjusted by varying the ratio of melting agent to refining agent, and these agents can be applied in different application steps. In particular, for a particular region of a subsequent layer, a first volume (which may also be expressed as a flow rate, mass, concentration, etc.) of the melting agent and a second volume of the refining agent may be determined based at least in part on the measured temperature. The volume of the melting agent and the refining agent may be determined with reference to a predetermined temperature for the subsequent layer prior to melting. Thus, the previously described block 112 of selectively applying a printing agent to subsequent layers may include: a first volume of a melting agent is selectively applied to a particular region of a subsequent layer, and a second volume of a refining agent is selectively applied to the particular region.

Figure 2c shows a heat map 200c of a subsequent layer of build material after application of the melting agent and just prior to the onset of melting. As shown, the cooling effect of the molten agent causes the previously hotter portion 204a to cool to a lower temperature than the surrounding build material to form a cooler portion 204 c.

Fig. 2d shows the heat map 200d after melting of subsequent layers. As shown, the locally cooler portion 204c counteracts the increased heat input over the region during melting so that the melted region has a uniform temperature.

As previously mentioned, the application of the printing agent may be otherwise controlled so as to provide a local temperature change prior to melting. The resulting temperature need not be uniform over the melt area, and different temperature profiles may be selected.

Fig. 3 is an example of an additive manufacturing device 300 that includes a temperature sensor 310 and processing circuitry 312. A build platform, which may be a removable component (e.g., provided as part of a cart), may be provided to support the layer of build material in use of the additive manufacturing apparatus 300. A build material distributor 302 may also be provided to form successive layers of build material on a build platform during a layer-by-layer additive manufacturing process. For example, the build material dispenser may include rollers to spread the build material over the build platform 314. In some examples, the removable component on which build platform 314 is provided may also include a source of build material, and may include a mechanism to lift and prepare the build material so that the build material dispenser can deploy the build material on build platform 314.

Temperature sensor 310 (which may be a thermal camera, a thermal imaging array, or the like) measures the temperature of the molten region and the temperature of the non-molten region of the first layer of build material. In some examples, the temperature sensors 310 may measure temperatures at multiple locations (e.g., thermal imaging pixels) on the layer of build material. The plurality of locations may include a plurality of locations within a molten region and a plurality of locations within a non-molten region.

The processing circuitry 312 includes a temperature control module 316. The temperature control module 316 is configured to control the temperature of the build material of the subsequent layer prior to melting based on the temperature of the melted region of the first layer and the non-melted temperature measured by the temperature sensor 310. The temperature control module 316 determines a pre-heat setting for the subsequent layer in response to the measured temperature of the non-melted regions of the first layer and determines printing instructions for applying a printing agent to the subsequent layer in response to the measured temperature of the melted regions of the first layer so that the pre-heated build material is at a predetermined temperature prior to melting.

The print instructions determined by the temperature control module 316 may be used to control a printing agent applicator (not shown). The printing agent applicator can be controlled to selectively print printing agent onto a layer of build material on the build platform in response to the print instructions. For example, the printing agent applicator may comprise a printing head (e.g. an inkjet printing head) and may apply the printing agent as a liquid, e.g. transported one or more times on the building platform.

The preheat setting determined by the temperature control module 316 may be used to control a preheat device (not shown). The preheating device preheats the layer of build material to a preheating temperature, which is lower than the melting temperature, according to the preheating setting. For example, the preheating apparatus may include an array of preheating lamps disposed above the build platform 314 to heat the build material to a preheating temperature. The apparatus may also include an energy source, which may be a heating lamp, that raises the temperature of the preheated build material above the melting temperature over a portion of the layer to form a molten region and a non-molten region.

Temperature control module 316 can control the preheating device such that the build material is maintained at the preheating temperature. In particular, temperature control module 316 can ensure that the temperature of the build material does not exceed the preheat temperature, such that inadvertent melting of the build material is avoided. The temperature control module 316 can adjust the temperature of the build material before melting by applying a printing agent to correct the temperature profile of the melted region after melting.

In some examples, the temperature control module 316 may be arranged to modify predetermined control data (i.e., preheat settings and print instructions) in response to measured temperatures of the molten and non-molten regions.

The temperature sensor 310 may also be used to control other aspects of the apparatus, for example to determine when to cool the generated object. The temperature sensor 310 may also be used to measure the temperature of other components of the additive manufacturing device, such as the temperature of a liquid trap, web wipe, or drop detector.

Fig. 4 is an example of a machine-readable medium 400 associated with a processor 402. The machine-readable medium 400 includes instructions that, when executed by the processor 402, cause the processor 402 to determine a pre-heat setting for a subsequent layer of build material in a layer-by-layer additive manufacturing process and determine printing instructions for applying a printing agent to the subsequent layer. The pre-heat setting is determined in response to a measured temperature of a non-melted region of a previous layer, and the print instructions are determined in response to a measured temperature of a melted region of a previous layer so that a temperature of the pre-heated build material is a predetermined temperature prior to melting.

In some examples, the printing instructions (and optionally the preheat setting) may form part of printing instructions derived from a particular layer of the object being formed. Determining control data (i.e., preheat settings and/or print instructions) may include modifying predetermined control data. The predetermined control data may be generated based on a predicted thermal model of the object being formed. The measured temperature may be compared to a predicted temperature and the deviation from the predicted temperature used to make adjustments to the control data.

The preheat setting may be a setting for preheating an array of lamps. In particular, the setting may be a duty cycle setting. The printing instructions may include timing information that schedules the order in which the printing agents are applied prior to fusing. The printing instructions may also include information about the printing agent itself, such as volume (i.e., drop size/rate), concentration, type, and the like. The printing instructions may be used to change the temperature of the region prior to melting in order to provide a desired temperature after melting.

In the case of a modification of the printing instructions acting on the scheduling of the application of the printing agent, it may also be necessary to take into account the influence of other regions of the layer. Thus, the machine-readable medium 400 may include instructions to seek an optimal solution that achieves a predetermined local temperature on a portion of the layer while minimizing impact on other areas of the layer.

In some examples, the adjustment of the control data may be determined using a threshold-based approach or a more complex approach such as a calculation based on proportional-integral-derivative (PID) control or by following a statistical approach (e.g., based on machine learning).

Examples in this disclosure may be provided as methods, systems, or machine-readable instructions, e.g., any combination of software, hardware, firmware, etc. Such machine-readable instructions may be embodied on a computer-readable storage medium (including but not limited to disk storage, CD-ROM, optical storage, etc.) having computer-readable program code embodied therein or thereon.

The present disclosure is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus, and systems according to examples of the disclosure. Although the above-described flow diagrams illustrate a particular order of execution, the order of execution may differ from that depicted. Blocks described with respect to one flowchart may be combined with blocks of another flowchart. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by machine readable instructions.

The machine-readable instructions may be executed by, for example, a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to implement the functions described in the specification and figures. In particular, a processor or processing device may execute machine-readable instructions. Accordingly, functional modules of an apparatus may be implemented by a processor executing machine-readable instructions stored in a memory or a processor operating according to instructions embedded in logic circuits. The term "processor" is to be broadly interpreted as including a CPU, processing unit, ASIC, logic unit, or programmable gate array, etc. The methods and functional modules may all be performed by a single processor or distributed among multiple processors.

Such machine-readable instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to operate in a particular mode.

The machine-readable instructions may also be loaded onto a computer or other programmable data processing apparatus to cause the computer or other programmable apparatus to perform a series of operations to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus implement the functions specified in the flowchart and/or block diagram block or blocks.

Furthermore, the teachings herein may be implemented in the form of a computer software product stored in a storage medium and comprising a plurality of instructions for causing a computer device to implement the methods described in the examples of the present disclosure.

Although the methods, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the disclosure. It is therefore intended that the methods, apparatus and related aspects be limited by the scope of the appended claims and equivalents thereof. It should be noted that the above-mentioned examples illustrate rather than limit what is described herein, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. Features described with respect to one example may be combined with features of another example.

The word "comprising" does not exclude the presence of elements other than those listed in a claim, "a" or "an" does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

Features of any dependent claim may be combined with features of any independent claim or other dependent claims.

Claims

1. A method, comprising:

measuring a temperature of a molten region and a temperature of a non-molten region of the first layer of build material;

determining a pre-heat setting for a subsequent layer of build material in response to the measured temperature of the non-molten region of the first layer;

determining printing instructions for applying a printing agent to the subsequent layer of build material, wherein, in response to the measured temperature of the melted region of the first layer, the application of printing agent specified by the printing instructions for the subsequent layer causes the temperature of the preheated build material to be a predetermined temperature prior to melting;

forming the subsequent layer of build material;

preheating the subsequent layer of build material according to a preheating setting; and

selectively applying the printing agent to a subsequent layer based on the printing instructions.

2. The method of claim 1, wherein the temperature of the non-molten zone is measured at a plurality of locations within the non-molten zone.

3. The method of claim 2, wherein a preheat setting is determined for each of the plurality of locations.

4. The method of claim 1, wherein the preheat setting is a duty cycle of a preheat lamp.

5. The method of claim 1, wherein the measured temperature of the non-molten region is compared to a predetermined preheat temperature, and wherein the preheat setting for the subsequent layer is determined based on a difference between the measured temperature and the predetermined preheat temperature.

6. The method of claim 1, wherein determining printing instructions for the subsequent layer comprises: modifying the predetermined print instructions for the subsequent layer.

7. The method of claim 1, wherein the temperature of the molten zone is measured at a plurality of locations to form a temperature profile, and wherein the temperature profile is compared to a predicted temperature profile.

8. The method of claim 1, wherein determining printing instructions for the subsequent layer comprises: determining a schedule for applying printing agent to the subsequent layer such that a temperature of the preheated build material is the predetermined temperature prior to melting.

9. The method of claim 1, wherein determining printing instructions for the subsequent layer comprises: determining a printing agent type or composition such that a temperature of the preheated build material is the predetermined temperature prior to melting.

10. The method of claim 1, further comprising: the molten and non-molten regions are identified based on temperature measurements or based on a model of the object.

11. An additive manufacturing device, comprising:

a temperature sensor for measuring a temperature of a molten region and a temperature of a non-molten region of the first layer of build material; and

a processing circuit, comprising:

a temperature control module for controlling a temperature of a build material of a subsequent layer prior to melting based on a temperature of a melted region and a temperature of a non-melted region of the first layer measured by the temperature sensor;

wherein the temperature control module determines a pre-heat setting for a subsequent layer in response to the measured temperature of the non-melted region of the first layer and determines printing instructions for applying a printing agent to the subsequent layer in response to the measured temperature of the melted region of the first layer so as to bring the pre-heated build material to a predetermined temperature prior to melting.

12. The additive manufacturing device of claim 11, wherein the temperature sensor comprises a thermal imaging camera.

13. A machine-readable medium comprising instructions that, when executed by a processor, cause the processor to:

determining a pre-heat setting for a subsequent layer of build material during a layer-by-layer additive manufacturing process; and

determining printing instructions for applying a printing agent to the subsequent layer;

wherein the pre-heat setting is determined in response to a measured temperature of a non-melted region of a previous layer, and the printing instructions are determined in response to a measured temperature of a melted region of the previous layer so as to cause the temperature of the pre-heated build material to be a pre-heat temperature prior to melting.

14. The machine-readable medium of claim 13, wherein the printing instructions comprise a schedule for applying a printing agent onto the subsequent layer of build material.

15. The machine-readable medium of claim 14, further comprising instructions that when executed by a processor cause the processor to: an optimal schedule is obtained that provides a desired temperature profile across the layer prior to melting.